Peroxidase and polyphenol oxidase activities in Cyperus esculentus leaves following glyphosate applications

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Abstract
Following a 2‐week treatment with glyphosate [N‐(phosphonomethyl)glycine] changes in peroxidase (EC 1.11.1.7) and polyphenol oxidase (PPO; EC 1.14.18.1) activities of yellow nutsedge (Cyperus esculentus L.) plants, were determined. Glyphosate caused significant increases of both activities. Isoelectric focusing gave 3 species (F1, F2 and F3) of peroxidase activity, at pl 3.8, 4.4 and 4.8, and 4 species (Fa, Fb, Fc and Fd) of PPO activity at pl 7.0, 7.5, 7.8 and 9.5. The activity of the 4 active forms of PPO increased with increasing glyphosate dose up to 10−2M. The effect of the herbicide on the 3 fractions with peroxidase activity was to change their relative activities. Highest F1 activity was found in control plants whereas the F2 fraction was the predominant form in the plants treated with glyphosate at 10−2M and the highest F3 activity occurred in plants treated with 5 × 10−3M glyphosate. The increased PPO activity could produce phytotoxic o‐quinones, and variations in peroxidase isoenzymes activity could enhance isoperoxidases with lignin biosynthetic activity.